The invention relates to a granulating device with a cutting knife head for cutting strands of melt into granules in a granulator housing. A perforated plate with die openings, from which strands of melt can be extruded into the granulator housing, projects into the granulator housing.
The cutting knife head, which has at least one cutting knife arranged radially on its outer circumference, is driven by a rotating drive shaft, wherein the cutting knife cuts the strands of melt emerging from the die openings to form granules. In this process, the granules are cooled by a fluid that enters the granulator housing through a first coolant inlet, and are discharged with the coolant from an outlet in the form of a mixture of coolant and granules.
Granulating devices of this nature are known to persons having ordinary skill in the art. Many of these devices use water as the coolant, and typically a coolant inlet is composed of an opening in a hollow drive shaft through which coolant enters the granulator housing and exits through the outlet of the granulator housing with the granules.
One disadvantage of the prior art is the limited cross-section of the coolant inlet in the hollow drive shaft of the cutting knife head, which restricts coolant flow and thus the amount of coolant delivered per unit time. This creates the risk that granules are not adequately cooled before they are delivered to the outlet, which can lead to clumping and sticking at the walls of the granulator housing and at the cutting knife head.
Another disadvantage is that coolant feed for discharging the granules cannot be regulated independently of the coolant feed to the cutting knife head, so that in the event of excessive central coolant feed for reliable discharge of the granules from the granulating device, there is a risk of the melt strand freezing in the die openings of the perforated plate. This risk is exacerbated due to the fact that the entire coolant flow consisting of the granule discharge flow and granule cooling flow in the prior art typically strikes the perforated plate directly through a discharge port that opens out in a funnel shape in the hollow drive shaft.
In addition, underwater granulating devices for thermoplastic plastics are known to persons having ordinary skill in the art. In these devices, the cutting knife head is typically concentrically enclosed by a hood. Typically, one part of cooling water flow is directed around the outside of the hood and a second part of cooling water flow is delivered to the cutting knife head through an opening in the hood. Located in the cutting knife head are bores that provide the cooling water that flows into the hood for direct granule cooling. The cooling water that flows outside around the hood is provided for the purpose of discharging the granules from the granulating device.
One disadvantage of this prior art underwater device is that the granule discharge flow for discharging the granules from the granulator housing cannot be controlled separately from the granule cooling flow that is intended to cool the granules directly during cutting, since the two coolant inlets are located in one common coolant inlet pipe. With this prior art device it is not possible to create an optimum balance between a granule discharge flow and a granule cooling flow in order to prevent clumping of the granules in the granule discharge flow in the event of insufficient cooling of the granules, and to avoid freezing of the melt strand in the die openings of the perforated plate in the event of excessively high granule cooling flow.
Furthermore, devices for the cutting, cooling, and removal of granules are known to persons having ordinary skill in the art. Typical designs utilize a drive shaft of a cutting knife head which is entirely or partially hollow in design and serves as a feed pipe for the cooling water and discharge water, and the cutting knife head has blade arms that likewise are hollow in design so that the cut-off granules entering the blade arm can be carried away therein with a water flush.
This type of granulating device has the disadvantage that the cutting knife head consisting of blade arms is extremely complex in its construction and the cross-section of the hollow drive shaft with the cutting knife head is limited, thus restricting the amount of coolant per unit time and allowing for a risk that the granules are not adequately cooled before they are delivered to an outlet, which can lead to clumping and sticking, both in the cutting blade arms and in the granulator housing.
Secondly, the coolant feed for discharging granules cannot be regulated independently of the coolant feed to the cutting knife head, so in the event of excessive central coolant feed for reliable discharge of the granules from the granulating device, there is a risk of the melt strand freezing in the die openings of the perforated plate, especially since the entire coolant flow consisting of the granule discharge flow and granule cooling flow is carried past the die openings of the perforated plate in this granulating device.
There is a need for a granulating device that ensures reliable control of a granule discharge flow for discharging the granules from the granulator housing, without sticking or clumping of the granules at walls and at the cutting knife head occurring as a result of inadequate coolant throughput in a granule discharge flow, and control of a granule cooling flow independent thereof that permits cooling directly at the cutting of the granules from the melt strands without the risk that freezing of the melt can occur in the die openings of the perforated plate.
The present embodiments meet this need.
The present embodiments are detailed below with reference to the listed Figures.